1. Field of the Invention
This invention relates to an improvement in the process for producing peracetic acid by the liquid phase oxidation of acetaldehyde with oxygen or an oxygen-containing gas under atmospheric or superatmospheric pressure.
More particularly, this invention provides an economical and efficient process for the large scale production of peracetic acid in high yields. This invention overcomes two problems encountered in prior processes, namely, the provision of a large heat transfer area per unit volume of the reactor and the maintenance of good gas liquid contact. The solutions of these two problems have usually been considered to be incompatible with each other. In addition, the invention provides a substantially unidirectional or piston-like flow state in the reaction system.
2. Discussion of the Prior Art
It has been known in the art that peracetic acid can be produced by reacting oxygen or an oxygen-containing gas with a mixture of acetaldehyde and an organic solvent. For instance, German Patent No. 1,205,519 discloses a process wherein the said reaction is carried out under a total pressure of 10-100 atm. at a temperature of 20.degree.-60.degree. C. in the presence of a heavy metal salt, while maintaining the gas and liquid in a turbulent flow state, and various types of apparatus for carrying out this process are illustrated.
However, it is a matter of extreme difficulty, when carrying out this process using these types of apparatus on a large industrial scale, to establish compatibility between the removal of the oxidation reaction heat and good gas-liquid contact.
It has been made clear from a number of experimental results that the maintenance of a good gas-liquid contact state not only serves to promote the formation of peracetic acid, but also is necessary to avoid the by-production of acetic acid due to the successive reaction of the peracetic acid so formed with acetaldehyde. It is therefore not desirable, in view of the increased by-production of acetic acid and the consequent poor yield of peracetic acid with a reduced purity that would result, to use a cooling system external to and separate from the reactor for removing the reaction heat because the concentration of oxygen in the circulating reaction liquid becomes lowered to favor the formation of acetic acid. In a stirred tank-type reactor having no external reaction liquid circulation to a cooler, the bundle of cooling tubes or coils inserted inside the reactor for heat removal purposes often prevents the dispersion of bubbles throughout the tank so that the efficiency of gas-liquid contact becomes remarkably poor. It has also been proposed to use a bubble column or a jacketed small tubular coil-type reactor as an apparatus adapted for small scale production, but the application of these types of apparatus to large scale production is very troublesome, because several units of apparatus must be installed in parallel and the distribution of gas and liquid to each unit must be uniformly conducted.
We have made a comparative study of the data with respect to the above-mentioned various types of reactors, and have further carried out a detailed study on bubble column-type reactors for the purpose of achieving the efficient and economical manufacture of peracetic acid on a large scale in order that an improved bubble column-type reactor will be most suitable for attaining this purpose.
We have recognized, after conducting various experiments on small scale apparatus, that the use of a usual jacketed bubble column provides a lesser gas-liquid contact effect, i.e., a poorer reaction result, than the use of a reaction vessel provided with turbine-type stirring blades. The efficiency of the gas-liquid contact is further reduced if the removal of heat is conducted by inserting bundles of cooling tubes into a bubble column having a larger diameter. However, we have now discovered, after various experiments, that in order to overcome this difficulty, the maintenance of violent turbulent flow at every part within the column, while maintaining a substantially piston-like or unidirectional flow condition in the entire column, is most necessary for carrying out the reaction most efficiently. For this purpose, we have found that the use of a column-type reactor provided with vertical cooling tubes inserted therein and in which the shell side is used as the bubble column in combination with perforated partition plates provided so as to satisfy specific flow conditions, can attain an extremely advantageous result. The present invention is a result of this discovery.